The present invention relates to a process of recovery of oil for spent bleached earth. More particularly the invention relates to the recovery of palm oil from spent bleached earth or clay.
Spent bleaching earth is a solid waste material generated as part of the refining process in the vegetable oil industry worldwide. A typical vegetable oil refining process involved pretreatment of crude vegetable oil such as palm oil with phosphoric acid, followed by bleaching deodorization. The purifying treatment is designed to remove undesired free fatty acids, phophatides, glycerides, sterols, tocopherols, resinous and mucilaginous materials from the crude palm oil. Bleaching is done solely to reduce the colour of the oil and is done using bleaching earth or clay. This process is followed by deodorization, which is intended primarily for the removal of traces of constituents that give rise to flavours and odors.
The most common adsorbent used for bleaching is the bleaching earth or clay. Naturally occurring bleaching earth is bentonite or montmorillonite clay which when acid activated with sulfuric acid increases adsorption capacity. After the treatment of crude oil with phosphoric acid, the oil is treated with bleaching earth, which adsorbs the impurities. Subsequently the treated oil is separated from the bleaching earth by filtration mostly in batches. The spent bleaching thus separated from the oil contains gums and impurities along with significant amount of oil.
It is not economical to recover the oil from the spent bleaching earth due to the small amounts of bleaching for individual oil refineries. In some countries it is generally a practice to dispose of the spent bleaching earth in landfills where else in some other countries it is treated as hazardous and is disposed off accordingly as hazardous waste.
In countries or regions where the palm oil industry is very large there is large amount of spent bleaching earth generated in the refining of crude palm oil process. Thus there is a need for a process to recover the oil in the spent bleaching earth in an economical manner before disposing of the spent bleached earth.
The invention discloses a process to recover oil from spent bleaching earth recovered from vegetable oil refining process. Although the example described in this invention refers to palm oil, the technology can equally be used in the extraction of other vegetable oil from spent bleaching earth used in the refinery process of other vegetable oils, such as soyabean oil, peanut oil, sunflower oil, etc. The process involves three sub-processes comprising of reacting the spent bleaching earth with a solvent selected from a group consisting of toluene, acetone, xylene, isopropyl alcohol or n-hexane at a temperature between 35xc2x0 C. to 50xc2x0 C.; separating the solids and liquid from slurry formed in the previous step; and extracting oil from the liquid fraction obtained in the previous step. The separation of the solids and the liquid from slurry can be formed in two steps. The slurry mixture of solids and liquid is first separated into a solid fraction and a liquid fraction. The solid fraction so separated still contains a significant portion of oil. Therefore the solid fraction is reacted with some solvent. The next slurry of solids and liquids is again separated into a solid fraction and a liquid fraction.
More particularly the invention described a process where spent bleaching earth from crude palm oil refinery process is reacted with n-hexane at a temperature between 35xc2x0 C. to 50xc2x0 C. in an agitated reactor for about 15 to 45 minutes. The reaction in the agitated reactor allows the dissolution of oil into the solvent. The slurry concentration in the agitator is maintained between 5% to 50% weight. The slurry thus formed is led to gravity settlers having plates for settling of solids.
The thicker slurry from the settlers is then introduced to vacuum belt filter for separation of the clay/bleaching earth and miscelle. Alternatively the slurry from the agitator reactor can be filtered in porous metal filters in two stages to improve efficiency. About 30% to 35% by weight of slurry from agitator is fed to the porous metal filter to get a clear filtrate and a cake with 70% to 75% dryness. This separated cake is ten remixed with fresh and/or recycled hexane to recover further absorbed oil from the cake in another agitator reactor. The slurry from this agitator is then again separated in another porous metal filter to obtain deoiled bleaching earth with about 3% to 5% oil content.
The filtrate or the miscella from the settlers/porous metal filters is than distilled in a distillation plant, which is a combination of rising film and fall film evaporators. The n-hexane distilled off is condensed in condensers and recycled back for processes. The extracted oil is further sent to refining to remove free fatty acids (FM) in a normal deodorizer system. The spent bleaching earth after removal of significant portion of the oil is the desolventized in a loop system using steam to recover left over solvent. This process condition is maintained between 80xc2x0 C. to 110xc2x0 C. to ensure complete removal of solvent before being fed to the incinerator system.